Micro-Raman spectroscopy was used to study the formation of BaFe 12 O 19 (BaM) powders derived from water-in-oil microemulsion at different calcination temperatures. With increase in the calcination temperature, the Raman spectra of the BaM powders become narrower and stronger without apparent frequency shifts of the Raman bands. The calcination temperature dependence of the Raman spectra and the magnetic properties of the BaM powders result from the crystallization rather than size effect. Our results show that there is a strong correlation between the crystallinity and the magnetic properties, which could be explained in terms of the crystallization effect on the superexchange interaction between ferric ions. The ␥-Fe 2 O 3 phase occurred in the BaM precursor and the powder calcined at 500°C. The ␣-Fe 2 O 3 phase was developed in the powders calcined at 500, 600, and 700°C, which was not detected by x-ray diffraction. With increasing calcination temperature, the ␥-Fe 2 O 3 phase can either react with oxide containing barium to form the BaM phase or transform to the ␣-Fe 2 O 3 phase. The amount of ␣-Fe 2 O 3 decreases due to reaction with BaCO 3 to form BaM phase at higher calcination temperature.

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